Light guide, detector having light guide, and charged particle beam device

ABSTRACT

A charged particle beam device includes a scintillator and
         a light guide. The light guide has an incident surface configured to incident a light from the scintillator, an emission surface configured to emit a light incident from the incident surface, and a first surface configured to guide the light incident from the incident surface to a side of the emission surface. The light guide has a bent portion. The bent portion has a second surface configured to guide the light to the side of the emission surface in regions excluding a region between the incident surface and the emission surface.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.16/082,745, filed Sep. 6, 2018, which is a National Stage ofInternational Application No. PCT/JP2017/003884, filed Feb. 3, 2017,which claims priority from Japanese Patent Application No. 2016-069943,filed Mar. 31 2016, the disclosure of which are expressly incorporatedby reference herein.

TECHNICAL FIELD

The present invention concerns a light guide, a detector having thelight guide, and a charged particle beam device, and more in particular,it relates to a light guide for guiding light at high efficiency to aphotoreceiving element, a detector having the light guide, and a chargedparticle beam device.

BACKGROUND ART

A charged particle beam device for detecting charged particles obtainedby irradiation of a sample with a charged particle beam such as anelectron beam has a detector for detecting the charged particles. Forexample, in a case of detecting electrons emitted from a sample byscanning a sample, an electron beam of a positive voltage at about 10 kVis applied to an electron detector, thereby guiding the electrons to ascintillator of the charged particle detector. Light generated in thescintillator by collision of electrons is guided along a light guide,converted into electric signals by a photoreceiving element such as aphotomultiplier tube to form image signals or waveform signals.

Patent Literature 1 describes a light guide attached to a scintillator.Further, Patent Literature 1 describes a configuration of providing atilted surface to a light guide for guiding light emitted from thescintillator to a PMT (photomultiplier tube). Patent Literature 2describes a light guide using a material of high transparency, forexample, an acrylic resin. Further, the cited reference 2 shows a deviceof guiding light generated in a scintillator by way of a light guide andallow the light to enter a photoelectric conversion element including,for example, a photomultiplier tube or a semiconductor photoreceivingelement. Further, it describes a scintillator structure in which asurface on the side opposite to the incident surface of the electrons isformed as a tilted surface in order to guide light at high efficiency tothe light guide.

CITATION LIST Patent Literature

Patent Literature 1: U.S. Pat. No. 8,895,935

Patent Literature 2: Japanese Unexamined Patent Application PublicationNo. 2014-67256 (corresponding to USP Laid-Open Publication No. US2015/0214002)

SUMMARY OF INVENTION Technical Problem

On the other hand, light generated in the scintillator is guided throughthe light guide to the photoreceiving element, which includes lightcolliding against the wall surface of the light guide in the course ofreaching the photoreceiving element. The collided light goes byreflection toward the photoreceiving element, some of which transmits tothe outside of the light guide. When light can be guided to thephotoreceiving element while suppressing transmission of light to theoutside of the light guide, an SN ratio of the charged particle beamdevice can be improved. According to the light guide disclosed in PatentLiterature 1, light generated in the scintillator can be guided to thePMT by reflecting light generated in the scintillator at the tiltedsurface of the light guide on the side opposite to the scintillatorattaching surface. However, as described above, light colliding againstthe wall surface of the light guide includes light which mayoccasionally transmits therethrough without reflection to restrict highdetection efficiency. Further, it may be considered to make a relativeangle larger between the tilted surface on the side opposite to thescintillator attaching surface and the attaching surface, so as toreflect as much light incident to the tilted surface as possible. Inthis case, however, it may be considered that the size of the lightguide increases in the direction of the optical axis of an electronmicroscope, etc. and the member is not suitable as one being disposed ina restricted space inside a vacuum chamber.

According to the detector structure disclosed in Patent Literature 2,while light emitted from the lateral side of the scintillator can beguided to the photoreceiving element, light sometimes transmits from thesurface on the side opposite to the collision surface of the chargedparticles of the scintillator, which also poses a limit on highefficient detection.

A light guide, with an aim of effectively guiding light generated in ascintillator to a photoreceiving element at high efficiency, a detectorhaving the light guide, and a charged particle beam device are to beproposed.

Solution to Problem

For attaining the purpose described above, it is proposed, in oneaspect, a light guide for guiding light generated from a scintillator toa photoreceiving element, including: a scintillator containment portionformed of a first surface facing a surface opposite to a chargedparticle incident surface of the scintillator and a second surfacefacing a surface of the scintillator different from the surface oppositeto the charged particle incident surface; and a tilted surface forreflecting a light incident from the second surface to the inside of thelight guide.

For attaining the purpose described above, it is proposed, in anotheraspect, a detector including: a scintillator; and a light guide forguiding light generated from the scintillator to a photoreceivingelement, in which the light guide includes a concave portion formed of afirst surface facing a surface opposite to a charged particle incidentsurface of the scintillator and a second surface facing a surfacedifferent from the surface opposite to the charged particle incidentsurface of the scintillator, and a tilted surface reflecting lightincident from the second surface to the inside of the light guide, andthe scintillator is contained in the concave portion.

For attaining the purpose described above, it is proposed, in anotheraspect, a charged particle beam device including a detector fordetecting at least one of charged particles emitted from a sample basedon irradiation of a charged particle beam emitted from a chargedparticle source and charged particles generated by collision of chargedparticles emitted from the sample against another member, in which thedetector includes a scintillator and a light guide for guiding lightgenerated from the scintillator to a photoreceiving element, in whichthe light guide includes a concaved portion formed of a first surfacefacing a surface opposite to a charged particle incident surface of thescintillator and a second surface facing a surface different from thesurface opposite to a charged particle incident surface of thescintillator, and a tilted surface for reflecting light incident fromthe second surface to the inside of the light guide, and thescintillator is contained in the concave portion.

Advantageous Effects of Invention

According to the configuration, light generated from the scintillatorcan be guided at high efficiency to the photoreceiving element.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a view illustrating a structure of an electron microscope.

FIG. 2 is a view illustrating an example of light passage in ascintillator.

FIG. 3 is a view illustrating an example of a light guide having ascintillator containment space and a side prism.

FIGS. 4A to 4C explaining a modification of a side prism.

FIGS. 5A and 5B are views illustrating a structure of an electronmicroscope.

FIGS. 6A to 6D are views illustrating an example of a light guide havinga bent portion.

FIGS. 7A to 7D are views explaining an example of a light guide having atilted portion connecting a bent portion and a linear portion.

FIG. 8 is a view illustrating an example of fitting a cross sectionalshape of a bent portion by using an equation of a circle.

FIGS. 9A and 9B are views explaining a specific shape of the lightguide.

FIGS. 10A to 10C are views explaining a specific shape of the lightguide.

FIGS. 11A to 11C are views observing a light incident surface of thelight guide in various directions.

FIG. 12 is a view explaining a specific shape of the light guide.

FIG. 13 is a view explaining a specific shape of the light guide.

DESCRIPTION OF EMBODIMENTS

In the charged particle detector using the scintillator as the detectionelement, highly efficient detection of charged particles can be attainedby guiding light generated inside the scintillator at high efficiency.On the other hand, the scintillator in the sterical shape has aplurality of surfaces and emits light from all surfaces of thescintillator not having a reflection material of reflecting light, butlight emitted from the scintillator surface not facing the light guidecannot be guided. That is, only the light emitted from a portion of thesurface can be incident to the light guide. Further, in a case where thelight guide is not linear but has a bent portion, light leaks in thebent portion and does not reach the photoreceiving element. Accordingly,light emitted from the scintillator cannot be propagated sufficiently tothe photoreceiving element. That is, in the optical system using thelight guide, the ratio of light reaching the photoreceiving elementrelative to light emitted from the scintillator (light utilizationefficiency) is often low.

A light guide for improving the light utilization efficiency is to bedescribed. In this embodiment, a charged particle beam device providedwith a detector using a scintillator as a detection element and having alight guide between the scintillator and the photoreceiving element isto be described. In the following example to be described below, anexample of an electron microscope, in particular, a scanning electronmicroscope is to be explained. However, this is not restrictive but theexamples to be described below are applicable also to other chargedparticle beam devices such as a scanning ion microscope using an ionbeam. Further, the examples are applicable also to a measuring device,an inspection device, an observation device, etc. for a semiconductorpattern using a scanning electron microscope.

The scintillator in the present specification means an element thatgenerates light upon incidence of a charged particle beam. Thescintillator referred to in the present specification is not restrictedto those illustrated in the examples but can be in various shapes andstructures.

First Embodiment

FIG. 1 is a view illustrating a basic configuration of an electronmicroscope 1. FIG. 1 is a view observing an electron microscope from theside, and FIG. 2 and FIG. 3 are detailed views of a scintillator 5 and alight guide 3. A primary electron beam 100 emitted from an electronsource 2 irradiates on a sample 50, from which secondary particles 101such as secondary electrons or reflected electrons are emitted. Thesecondary particle 101, after collision against a signal particlecontrol plate 6, is incident to the scintillator 5. Particles aftercollision against the signal particle control plate 6 are sometimesreferred to as tertiary particles but, for simplifying the explanation,secondary particles emitted from the sample 50 and secondary electronsgenerated by collision of secondary particles emitted from the sampleagainst the signal particle control plate 6 are inclusively referred toas the secondary particles. In this embodiment, a scintillator 5 havinga circular secondary particle incident surface is to be explained. Inthis example, a columnar scintillator having a smaller size in theheight relative to the size of the secondary particle incident surfaceis to be explained as an example. When the secondary particles 101 areincident to the scintillator 5, luminescence occurs in the scintillator5. Luminescence in the scintillator 5 is guided by way of a light guide3 and converted by a photoreceiving element 4 into electric signals.Hereinafter, the scintillator 5, the light guide 3, and thephotoreceiving element 4 are sometimes collectively referred to as adetection system.

In the case of the scanning electrode microscope, signals obtained atthe photoreceiving element 4 are stored in a memory medium such as aframe memory in synchronization with scanning of the primary electronbeam (electron beam). By display of brightness in accordance with anamount of signals obtained at an image position (pixel) corresponding toan electron beam irradiation position, a contrast image can be formed ina scanning region. In FIG. 1, an electron optical system for focusing aprimary electron beam 100 to irradiate the sample, that is, a reflector,a lens, a diaphragm, an objective lens, etc. is not illustrated.

Inside of an electron optical column 60 constituting the electronoptical system is kept in a vacuum state and configured such that a beampasses through the vacuum space. Further, a sample 50 is placed on asample stage for moving the sample at least in X-Y direction (assumingan ideal optical axis of the primary electron beam as Z direction), andthe sample 50 and the sample stage are located in a sample chamber 61.The sample chamber 61 is generally kept in a vacuum state duringelectron beam irradiation. Further, the electron microscope is providedwith a control unit for controlling the operation of the entire systemand each part, a display unit for displaying images, an input unit forinputting a user's operation instruction to the electron microscope,etc. although not illustrated. Further, an unillustrated negativevoltage applying power source is connected to the sample stage, whichcan form a deceleration electric field to the electron beam. Since thedeceleration electric field to the electron beam is an accelerationelectric field to the secondary particles emitted from the sample(secondary electrons and backward scattering electrons), the secondaryparticles, etc. are accelerated in the direction to the electron source2 and collide against the signal electron control plate 6, etc.

The electron microscope is an example of configuration and otherconfigurations may also be applied so long as the electron microscopehas a scintillator 5, a light guide 3, and a photoreceiving element 4.In the example of FIG. 1, an example of detecting new secondaryparticles generated based on the collision of the secondary particlesagainst the signal electron control plate 6 (tertiary particles) isexplained, but it may be configured such that a scintillator is locatedat a position of the signal electron control plate 6 and light generatedfrom the scintillator is guided to the photoreceiving element through alight guide.

Further, the secondary particles 101 include also transmissionelectrons, scanning transmission electrons, etc. Further, although onlyone detector is shown for the sake of simplification, a plurality ofdetectors may also be provided. A detector for reflection electrondetection and a detector for secondary electron detection may beprovided separately or a plurality of detectors may be provided fordiscrimination and detection of an azimuth angle or an elevation angle.

Then, the scintillator 5 of this embodiment is to be described indetails with reference to FIG. 2. In FIG. 2, the front direction DF is adirection in parallel with a normal line on the bottom of a columnarscintillator 5 (referred to as an upper bottom 5 c in order todistinguish the upper and lower bottoms of a column), which is adirection along which particles 101 propagate. The side direction DS isa direction perpendicular to the front direction DF. The drawing is aview of observing the columnar scintillator 5 along the side directionDS. The scintillator 5 includes a light emission part 5 a that convertsthe energy of the incident secondary particle 101 to light and generateslight and a conduction layer 5 b for applying a voltage to thescintillator 5. The conduction layer 5 b is a layer formed by laminationover the light emission part 5 a which is an Al layer in thisembodiment. However, it may suffice that the scintillator 5 has a lightgeneration part 5 a and the configuration is not limitative to this.

The material of the light emission part 5 a includes semiconductors(GaN, Si, SiC), ceramic phosphors YAG (Y₃Al₅O₁₂:Ce), YAP (YAlO₄:Ce),powdery phosphors Y₂SiO₅:Ce, which are used being deposited on asubstrate, etc. An example of the semiconductor scintillator includes asemiconductor having, as a photoconversion portion, a structure offorming a quantum well by laminating InGaN and GaN. The InGaN layer andthe GaN layer are laminated to the incident direction of the chargedparticles.

The secondary particles 101 incident to the scintillator 5 are passedthrough the conduction layer 5 b and converted into light in the lightemission part 5 a, and the converted light is propagated through thelight emission part 5 a and emitted to the outside of the scintillator5. Since the conduction layer 5 b functions as a reflection member tothe light, light is emitted from all of the surfaces having noconduction layer 5 b.

Examples of light were shown in the drawing as RayF1, RayF2, RayS1, andRayS2. RayF1 and RayF2 are examples emitting from the upper bottomsurface 5 c in the front direction DF and RayF2 is an example reflectedon and emitted from the conduction layer 5 b. RayS1 and RayS2 areexamples of propagating in the side direction DS and emitting from theside 5 d. RayS2 shows an example of totally reflecting at the upperbottom 5 c, reflecting at the conduction layer 5 b and emitting from theside 5 d, which is an example of being guided in the light generationpart 5 a and emitted from the side 5 d. Since the light generation part5 a has a refractive index higher than that of air, a portion of thelight is guided while totally reflecting at the surface of thescintillator 5.

The ratio between the sum of light emitting from the side 5 d (sideemission amount 1 s) and the sum of light emitting from the upper bottomsurface 5 c (surface emission amount 1 p) depends on the inner structureof the scintillator 5. In a case of using a scintillator including asemiconductor or a ceramic phosphor material or a case of using asubstrate with deposition of a powdery phosphor material as ascintillator and taking out and utilizing light also from the substrate,the refractive index of materials is generally larger than 1.5, and thetotal reflection angle for the surface of the scintillator 5 is about 40degrees at a refractive index of 1.5. Therefore, about 75% or more ofthe light incident to the surface undergoes total reflection. When theinside of the light emission part 5 a has a structure tending to causescattering, light sometimes causes random reflection to reach thesurface again and emit from the surface. Since the scintillatordescribed above is in a configuration of causing less opticalscattering, light is guided to the side 5 d, and a great amount of lightemits also from the side 5 d. In a case of a scintillator 5 using GaN asthe material according to simulation, lp:ls=about 1:1 for 0.5 mm inheight and 9 mm in diameter of the column. Further, even when atechnique is introduced which introduces a pattern structure of apyramid, corn, etc. or a pattern structure about at or less than thelight wavelength in the light emission part 5 a, and suppresses lightguidance by scattering, thereby improving the surface light emissionamount 1 p from the upper bottom 5 c, lp:ls=about 7:3. Accordingly, itis important to dispose also the lateral side emission amount is by thelight guide, thereby improving the light yield.

Then, the light guide 3 is to be explained with reference to FIG. 3.FIG. 3 is a cross sectional view of the light guide 3 and the lightguide 3 has a rotational symmetric shape with respect to a center lineCL. As a material for the light guide 3, PMMA resin, cycloolefin polymer(COP) resin, silica, quartz, etc. may be used. However, the presentinvention is not restricted to the material.

A separation flange 3 c is provided to the side 3 d of the light guidecolumn for separating the vacuum inside the electron optical column 60and the atmospheric air in the outside. The separation flange 3 cdepends or does not depend on the structure of the electron microscope1. In this embodiment, since the photoreceiving element 4 is disposedoutside of the electron optical column 60 and the scintillator 5 isdisposed inside the electron optical column 60, the separation flange 3c is provided to the light guide 3.

The emission surface 3 b of the light guide 3 is circular which is asurface opposed to the photoreceiving element 4. The surface facing theupper bottom 5 c of the scintillator 5 is an incident surface 3 a (firstsurface) of the light guide 3. The light incident from the incidentsurface 3 a is partially absorbed in the light guide 3, but most of itreaches the emission surface 3 b. Ray F3 is an example of light incidentfrom the incident surface 3 a to the light guide and emits from theemission surface 3 b.

A portion disposed opposing to the side 5 d of the scintillator 5 is aside prism 3 e, and the side prism 3 e has a side prism incident surface3 e 1 (second surface) which opposes to the side 5 d of the scintillator5 and to which light is incident from the side 5 d. The side prismincident surface 3 e 1 is a side wall surface having a direction ofplane in the direction different from the incident surface 3 a of thelight guide 3.

Further, the incident surface 3 a of the light guide 3 and the sideprism incident surface 3 e 1 define a containment space surrounding thescintillator 5. For receiving all the light from the scintillator 5, thecontainment space is formed preferably so as to oppose to all thesurfaces from which the light of the scintillator 5 emits. However, evenif the containment space is configured such that the opposing surface isformed only to a portion of the surface from which light of thescintillator 5 emits, it provides an effect of improving the lightutilization efficiency so long as it has a side wall surface.

The side prism 3 e has a reflection surface 3 e 2 (tilted surface) ofreflecting the light incident from the side prism incident surface 3 e 1so as to direct the light to the emission surface 3 b. The reflectionsurface 3 e 2 is formed so as to surround the side prism incidentsurface 3 e 1. RayS3 is an example of light incident from the incidentsurface 3 e 1 to the side prism 3 e, totally reflecting at thereflection surface 3 e 2 and emitting from the emission surface 3 b.This embodiment has a configuration that the reflection surface 3 e 2has a predetermined angle θ_(e2) relative to the direction of the normalline 3 eN on the side prism incident surface 3 e 1, thereby capable oftotally reflecting light incident in the direction of the normal line 3eN on the side prism incident surface 3 e 1.

Total reflection occurs only in a case where the incident angle of lightto the reflection surface 3 e 2 is larger than the critical angle θ_(c).Preferably, the incident light also includes light at angles other thanthe angle in the direction of the normal line 3 eN, and a reflectionmember is preferably provided to the surface of the reflection surface 3e 2 in order to reflect more light. The reflection member includes, forexample, aluminum, silver, multilayered reflection films, etc.

With respect to the angle θ_(e2), it is preferably larger than 20degrees and smaller than 70 degrees with a viewpoint of reflection inthe direction of the emission surface 3 b. However, the upper limit ofthe angle depends on the shape of the light guide 3, and the angle takesother values in a case of a bent light guide 3, for example. Since thereflection light can be propagated to the emission surface 3 b byproperly setting the angle θ_(e2), this provides an advantageous effectof improving the light unitization efficiency.

Further, the angle θ_(e2) for reflection in the direction of the normalline 3 aN on the incident surface 3 a does not depend on the shape ofthe light guide 3 and is preferably within a range of 45 degrees±15degrees. Since most of light propagating in the direction of the normalline 3 aN on the incident surface 3 a does not leak from the portionother than the emission surface of the light guide 3 but can be guidedthrough the light guide 3, this can provide an advantageous effect ofimproving the light utilization efficiency.

By the side prism. 3 e, since the emission light from the side 5 b ofthe scintillator 5 can also be incident to the light guide 3 and reflectat the reflection surface 3 e 2 to the emission surface 3 b and morelight can be propagated to the photoreceiving element 4, this canprovide an advantageous effect of improving the light utilizationefficiency. Usually, in the scintillator, the surface in the directionof the thickness of the surface in the direction perpendicular to theincident surface (side) is sufficiently smaller than the size in thedirection of the plane of the incident surface of the charged particles.Accordingly, it is configured such that light emitted from the upperbottom surface 5 c is guided in the direction of the center line CL ofthe light guide (optical channel direction of the light guide) with noreflection using the prism or the like and guide light emitted from theside of the scintillator in the direction of the light guide opticalchannel accompanying reflection of using the side prism. That is, in acase of forming a containment space of the scintillator 5 in the lightguide 3, the size in the direction of the height of the side prismincident surface 3 e 1 is defined smaller than that of the incidentsurface 3 a, and arranged so as to oppose the side 5 d of thescintillator 5 to the side prism incident surface 3 e 1 of the lightguide 3, and the upper bottom 5 c of the scintillator and the incidentsurface 3 a of the light guide 3, respectively.

With the configuration described above, the light emitted from each ofthe surfaces of the scintillator can be guided at high efficiency to thedetection element while decreasing the amount of light changing thepropagation direction by reflection in the light guide.

Then, modifications of the reflection surface 3 e 2 are to be explainedwith reference to FIG. 4. FIG. 4 is an enlarged cross sectional view forthe vicinity of the side prism 3 e.

FIG. 4(a) shows an example of attaching a reflection member 3 e 2R tothe surface of a reflection surface 3 e 2. By provision of thereflection member 3 e 2R, the light incapable of total reflection at thereflection surface 3 e 2 but transmits therethrough can also bereflected to improve the light utilization efficiency. Light RayS4 isloss light transmitting the reflection surface 3 e 2 in a case where thereflection member 3 e 2R is not present. If the reflection member 3 e 2Ris present, light is reflected and guided to the emission surface 3 b.The reflection member may be attached by various methods such as vapordeposition in addition to bonding, and this embodiment is not restrictedby the way of attachment. In this embodiment, the reflection member doesnot entirely cover the light guide but attached only to a portion of thelight guide (reflection surface). Since a usual reflection materialabsorbs a portion of light upon reflection, the material is not bondedto the side 3 d of the light guide where light reflects by plural times.The absorption ratio in a case of using a metal as the reflectionmaterial is about 5 to 15%. It is important that the side 3 d guideslight by total reflection without causing light absorption.

FIG. 4(b) shows a case where the shape of the reflection surface 3 e 2is not linear but a polygonal line. The propagation direction of lightis changed by plural reflections. As an example, an example of lightRayS5 was illustrated.

FIG. 4(c) shows a case where the shape of the reflection surface 3 e 2is not linear but a curve. The light propagation direction is changed byplural reflections. As an example, light RayS6 was illustrated. Theconfiguration of the curve may be considered to be various shapes suchas circular, elliptic, parabolic or hyperbolic. It is not restrictedonly to the curve but may be a combination of a curve and a polygonalline or a curve and a linear line. For the shape of the reflectionsurface 3 e 2, any shape of reflecting light so as to propagate to theemission surface 3 b can provide an advantageous effect of improving thelight utilization efficiency.

Second Embodiment

FIGS. 5 and 6 are views for explaining a second embodiment. Identicalportions or portions having identical functions with those of the firstembodiment are not explained. Further, portions carrying identicalreference numerals are those portions having similar functions. FIG.5(a) is a side elevational view of an electron microscope. FIG. 5(b) isa view of the electron microscope 1 in the direction of an arrow A inFIG. 5(a). Assuming a plane containing a dotted line B and the center ofthe emission surface as plane S1, FIG. 6(a) is a cross sectional view ofalight guide 3 in the plane S1. Further, the plane S1 is a surface alsocontaining the center of the incident surface 3 a.

An electron microscope as illustrated in FIG. 5 has no signal particlecontrol plate as illustrated in FIG. 1, and secondary particles 101 aredirectly incident to a scintillator 5. Further, when compared with theexample of FIG. 1, the shape of the light guide is different. In thelight guide 3 of this embodiment, since the incident surface 3 a and theemission surface 3 d are not faced (the scintillator emission surface isnot present in the direction of the normal line on the incident surfaceof the scintillator), a bent portion 3 f is provided in the light guide3.

For the sake of simplicity, only one detection system is shown butplural detection systems may be provided or another detection systemincluding a signal particle control plate may also be provided. Althoughnot illustrated in this embodiment, another detection system having asignal particle control plate is provided on the side nearer to thesample 50 than the illustrated detection system.

The electron optical system of this embodiment has an optical system inwhich a primary electron beam 100 emitted from an electron source 2 goesstraight to the sample 50, while the secondary particles 101 can be bentto the scintillator 5. Since the secondary particles 101 are in directincident to the scintillator 5, secondary particles 101 propagatinglinearly from the sample 50 can be detected at high sensitivity.

As shown in FIG. 5(b), the light guide 3 has a bent portion 3 f andlight is also guided to the emission surface 3 b while undergoingreflection in the bent portions 3 f and reaches the photoreceivingelement 4. The cross sectional shape is to be explained in details withreference to FIG. 6(a). The cross sectional shape generally includesthree portions. They are three portions including bent portions 3 f 1, 3f 2, tilted portions 3 g 1, 3 g 2 the shape of which changes moregradually than that of the bent portions, and linear portions 3 h 1, 3 h2.

The shape of the linear portion 3 h is a columnar shape having anemission surface 3 b as a bottom (a circle with radius r_(a), refer toFIG. 6(b)). A separation flange 3 c is provided to the linear portion 3h. By provision of the separation flange 3 c in the linear portion 3 h,the separation flange 3 c can be abutted vertically against the sidewall, etc. of the electron optical column 60 to suppress flowing ofatmospheric air into vacuum.

The tilted portion 3 g has a shape of connecting the bent portion 3 fand the linear portion 3 h. The cross sections 3 g 1, 3 g 2 are in theshape of moderately changing curves. The cross sectional shape is notrestricted to that of the curve but may be formed of a linear line, apolygonal line, a combination of curve and linear line or a combinationof curve and polygonal line.

The cross sectional shapes 3 f 1, 3 f 2 of the bent portion are arcshaving a central angle between 60 degrees and 89 degrees in thisembodiment. The cross sectional shape may be a curve somewhat deviatedfrom the arc, or may partially include an arc or a curve and partiallyinclude a linear or polygonal line. The bent portion is in a complicateshape for reducing the amount of light leaked from the surface of thebent portion to the outside of the light guide. The incident surface 3 ais in a shape shown in FIG. 6(c) in which cross sectional shapes 3 f 1and 3 f 2 are connected to the points D and E respectively. The lefthalf is a circle 3 a 1 and the right half is an ellipse 3 a 2 withrespect to the dotted line F as a boundary. The radius of the circle isr_(a) and one-half length of the short axis and that of the major axisof the ellipse are r_(a) and r_(b) respectively (r_(a)<r_(b)). Thecenter of the scintillator 5 is situated at a position substantiallyopposing the intersection between the dotted line F and a segmentconnecting the points D and E.

Assuming a plane perpendicular to the plane S1 and containing the dottedline C as a plane S2, the cross sectional shape of the light guide 3 atthe plane S2 is a circle identical with that of the emission surface 3b. The shape of the bent portion 3 f is a shape of connecting the crosssectional shape of the circle and that of the incident surface 3 a withthe cross sectional shapes 3 f 1, 3 f 2 as a contour. The shape of thebent portion can be prepared by lofting the shape of the circle and theincident surface 3 a with the cross sectional shapes 3 f 2, 3 f 2 as acontour using, for example, a usual 3D CAD (three-dimensional computeraided design system). FIG. 6(d) is a perspective view of the light guide3 in this embodiment. Reference numeral 3 i shows a portion for fixingthe light guide 3 and the scintillator 5.

The shape of the bent portion is to be described more in details withreference to FIG. 7. FIG. 7(a) is a cross sectional view in the plane S1for explaining the reason of light leakage in the bent portion 3 f. Inthis example, the tilted portion 3 g as in the light guide illustratedin FIG. 6 is not present. The shape of the incident surface 3 a or thatof the emission surface 3 b is a circle shown in FIG. 6(b), and thecross sectional shapes 3 f 1 and 3 f 2 in the bent portion are an arcwith the central angle of 90 degrees and starting from the incidentsurface 3 a. The bent portion 3 f and the emission surface 3 b areconnected by way of a linear portion 3 h. This is the simplest lightguide shape of connecting the incident surface 3 a and the emissionsurface 3 b.

Typical light path of leaking light is to be described with reference tothree examples of light. Light RayF5 is an example of reaching the crosssection 3 f 1 in the bent portion and transmitting the surface since theangle relative to the normal line 3N1 on the surface of reaching pointis smaller than the critical angle of total reflection. All the lightwith the angle of light between the normal line on the incident surface3 a and the angle upon emission from the incident surface 3 a beinglarger than the angle shown in the drawing transmits the bent portion 3f to cause loss.

Light RayF6 (shown by dotted line for distinguishing from other light)is an example of totally reflecting in the direction of the normal lineof the incident surface 3 a on the cross section 3 f 2 of the bentportion, reaching the cross section 3 f 1 of the bent portion, andtransmitting the surface since the angle relative to the normal line 3N2on the surface of the reaching point is smaller than the critical angleof total reflection. Light emitting from a position near the crosssection 3 f 2 of the bent portion reflects at the cross section 3 f 2 ofthe bent portion and leaks from the light guide 3 through a similarlight passage.

Light RayF7 is an example of light emitting from the incident surface 3a being tilted from the normal line on the incident surface 3 a to theemission surface 3 b, reaching the cross section 3 h 1 of the linearportion, and transmitting the surface since the angle relative to thenormal line 3N3 on the surface of the reaching point is smaller than thecritical angle of the total reflection. Light reaching the surfacehaving a normal line substantially in parallel with the normal line onthe incident surface 3 a has a high possibility of transmitting thesurface. The transmittance is in accordance with the Fresnel'stransmittance.

The light guide 3 shown in FIG. 6(a) is in a shape of suppressing suchlight leakage. The light guide shown in FIG. 7(b) is a light guide 3shown in FIG. 6(a) and the light leakage suppressing effect is to bedescribed with reference to the drawing. Main features of the lightguide 3 in FIG. 7(b) are that the radius of curvature at the crosssection 3 f 1 of the bent portion is larger compared with that in FIG.7(a), and the shape of the incident surface 3 a is a shape including theellipse where the major axis shown in FIG. 6(c) is in the direction ofthe emission surface. Since the radius of curvature for the crosssection 3 f 1 of the bent portion is large, the surface of the lightguide 3 that guides light to the emission surface 3 b is present inaddition to the region between the incident surface 3 a and the emissionsurface 3 b. The region between the incident surface 3 a and theemission surface 3 b is a region represented by the arrow DA in FIG.7(b). The dotted line shown by the arrow is an auxiliary line forshowing the region in which, in the drawing, the lower dotted line isaligned with the end of the incident surface 3 a and the upper dottedline is aligned with the end of the emission surface 3 b. In the lightguide with no tilted portion shown in FIG. 7(a), the surface of thelight guide 3 for guiding the light to the emission surface 3 b is notpresent except for the region. The fixing portion such as the separationflange 3 c is not a surface for guiding the light to the emissionsurface 3 b.

When the radius of curvature of the cross section 3 f 1 of the bentportion is large, total reflection tends to occur in the bent portion.Light RayF8 is light emitted from the incident surface 3 a at an angleidentical with that of the light RayF5 in which the incident angle tothe cross section 3 f 1 of the bent portion is larger than that of thelight RayF5 and undergoes total reflection. Since the radius ofcurvature is large, light is incident at a position where the normalline 3N4 at the light incident position to the arc is tilted greatlyfrom the normal line on the incident surface 3 a. Accordingly, theamount of light for total reflection in the bent portion increases toimprove the light utilization efficiency of the light guide.

Light RayF10 is light that emits from the incident surface 3 a at anangle identical with that of light RayF7. Since the radius of curvatureis large, light RayF10 is incident to the cross section 3 f 1 in thebent portion near the end point and is guided under total reflection.Since the normal line 3N6 at the cross section 3 f 1 in the bent portionnear the end point is tilted from the incident surface 3 a in thedirection opposing to that of the emission surface 3 b, the anglebetween the normal line 3N6 and the incident light is increased tendingto cause total reflection. Since the Fresnel reflectivity is improvedeven if the light does not show total reflection, the amount ofreflection light increases to improve the light utilization efficiencyof the light guide.

In a case where the scintillator 5 is a column of 9 mm in diameter, itwas confirmed by a light tracing calculation that the light utilizationefficiency was improved by 37% by defining the incident surface 3 a tothat of a circle of 10 mm in diameter, and by changing the radius ofcurvature for the cross sections 3 f 1 and 3 f 2 in the bent portionfrom 15 mm and 5 mm to 18 mm and 8 mm respectively.

Light RayF9 is light emitted from the incident surface 3 a at an angleidentical with that of light RayF6. Light RayF9 can reach the crosssection 3 g 1 of the tilted portion without reflection at the crosssection 3 f 2 by forming a portion of the incident surface 3 a as anellipse where the major axis is in the direction of the emission surfaceand displacing the cross section 3 f 2 of the bent portion toward theemission surface 3 b. Light RayF9 does not always cause total reflectionat the cross section 3 g 1. Since the angle between light RayF9 and thenormal line 3N5 is increased at the incident point on the cross section3 g 1 compared with the case of light RayF6, the Fresnel reflectivity isincreased, and the amount of guided light is increased to improve thelight utilization efficiency.

Then, the shape of the elliptic portion of the incident surface 3 a isto be described. For example, in a case where the radius of thescintillator 5 is 4.5 mm, and r_(a) and r_(b) are defined as 4.5 mm and5.5 mm respectively in FIG. 6(c), it was confirmed by the light tracingcalculation that the light utilization efficiency was improved byseveral % compared with the case of defining the incident surface 3 a asa circle of 9 mm in diameter. In this embodiment, the light utilizationefficiency has been improved by forming a portion of the incidentsurface 3 a to an ellipse and making the shape longer on the side of theemission surface, thereby transferring the cross section 3 f 2 towardthe emission surface. However, the embodiment is not restricted todefine a portion of the incident surface 3 a to an ellipse but it maysuffice that the shape is made longer on the side of the emissionsurface. In other words, it may suffice that the distance from thecenter of the scintillator 5 to the end of the incident surface 3 a isdifferent from the direction opposing to that of the emission surfaceand the distance in the direction of the emission surface is longer.

Then, the shape in which the bent portion 3 f is partially or entirelyformed into an arc is to be described with reference to FIGS. 7(c) and(d). The cross sectional shape 3 f 1 in the bent portion is an arcuateshape of this embodiment. The cross sectional shape 3 f 1C (shown bydotted line) is a cross sectional shape where the arc center CP1 ispresent within a plane SP (shown by dotted line) including the incidentsurface 3 a in which the tangential line rising from the incidentsurface 3 a of the cross sectional shape 3 f 1C is in parallel with thenormal line 3 aN on the incident surface. The cross sectional shape 3 f1C is a shape of a bent portion in a case of configuring a light guidewith no tilted portion shown in FIG. 7(a), and it can be said that thisis the simplest shape as the bent portion.

The cross sectional shape 3 f 1 is a configuration in which the centerCP2 of the arc is not present in the plane SP and is lower than theincident surface 3 a (direction parting from the light guide 3).Further, a tangential line 3 f 1T rising from the incident surface 3 aof the cross sectional shape 3 f 1 and a normal line 3 aN on theincident surface are in a shape having a predetermined angle θ_(t). Theangle θt is preferably in a range of about 2 degrees to 10 degrees witha viewpoint of improving the light utilization efficiency. The angle θtof the light guide 3 shown in FIG. 7(b) is 2.5 degrees. Further, thedistance between the center CP2 and the plane SP is 1 mm. The distanceis preferably within a range of about 0.3 mm to 5 mm.

In a case where the surface of the light guide 3 is divided along a lineinto a curved outer surface and a curved inner surface, the crosssectional shape 3 f 1 is contained in a curved outer surface startingfrom the end of the incident surface 3 a and the cross sectional shape 3f 2 is contained in the curved inner surface. In the configurationdescribed above, the curved outer surface has a tangential line tiltedfrom the normal line 3 aN on the incident surface to the side of theincident surface at a contact point between the curved outer surface andthe incident surface 3 a.

Light RayF11 is light emitting from almost the center of the incidentsurface 3 a to the bent portion in parallel with the normal line 3 aN onthe incident surface. The intensity of light generated from thescintillator 5 is generally highest in the direction and at theposition. Reference numerals 3 f 1N, 3 f 1CN respectively show normallines at the intersections between the cross sections 3 f 1 and 3 f 1Cand light RayF11. Angles θ₁, θ₂ are angles formed between the normalline 3 f 1N and light RayF11, and between 3 f 1CN and light RayF11respectively. FIG. 7(d) is a view for comparison between angles θ₁ andθ₂ in which intersections between light RayF11 and each of crosssections are aligned. As can be seen from the drawing, the angle θ₁ islarger than the angle θ₂. Accordingly, since the incidence angle oflight RayF11 to the cross section 3 f 1 is larger, the ratio of totallyreflecting optical fluxes is increased among the optical fluxes incidentto the light guide 3 and the Fresnel reflectivity is further increased,so that the light leakage is decreased to improve the light utilizationefficiency.

That is, the light utilization efficiency is improved in a case where aportion of the cross sectional shape 3 f 1 (desirably, a portion whereRayF11 is incident) is arcuate and the center CP2 of the arc is notpresent in the plane SP containing the incident surface 3 a. Further,the light utilization efficiency is improved in a case where thetangential line 3 f 1T rising from the incident surface 3 a of the crosssectional shape 3 f 1 and the normal line 3 aN on the incident surfaceare in a shape having a predetermined angle θ_(t).

It is preferred that the cross sectional shape 3 g 1 and the crosssectional shape 3 g 2 in the tilted portion are substantially inparallel as in this embodiment. Because, when the height of the lightguide decreases toward the emission surface 3 b as shown in FIG. 7(b),the incident angle to the cross sectional shape 3 g 1 is decreased onevery incidence of light to the cross sectional shape 3 g 1, while,since the incident angle to the cross sectional shape 3 g 2 increases onevery incidence of light to the cross sectional shape 3 g 2 (thephenomenon is reversed in a case where the height of the light guideincreases), the incident angle is compensated. Accordingly, thisprovides an advantageous effect that the incident angle upon initialincidence to the tilted portion 3 g does not change greatly in thecourse of the light guidance and the incident angle is decreased to lessthan the total reflection angle to suppress occurrence of light leakage.

In this embodiment, the cross sectional shapes 3 f 1, 3 f 2 in the bentportion are arcuate but this is not restrictive and they may be a curveor a polygonal line deviated from an equation of a circle. However, theouter cross sectional shape 3 f 1 of the bent portion is desirably aconfiguration to be partially fitted by using an equation of a circle,ellipse or hyperbola.

An example of fitting the cross sectional shape 3 f 1 in the bentportion by using an equation of a circle is to be explained withreference to the graph of FIG. 8. For the reference, the position of theincident surface 3 a was described in the graph. In the graph, the crosssectional shape 3 f 1 is described in the direction opposite to thecross sectional shape of the light guide described in FIG. 6 and FIG. 7.The abscissa represents a positional coordinate [mm] in parallel withthe incident surface and the ordinate represents the positionalcoordinate [mm] in the direction parallel with the normal line on theincident surface. The dotted line is an example of the cross sectionalshape 3 f 1 in the bent portion, which is not a complete arc. The solidline 3 iF is a result of fitting by the equation of a circle. The dottedline and the solid line are well aligned except for the vicinity of theend of the incident surface 3 a. The center P1 of the arc, etc. may bedetermined by using the result of fitting.

In this embodiment, a circle, a partial circle and an ellipse, or thelike is used for the shape of the incident surface 3 a and the emissionsurface 3 b, but the present invention is not restricted to them. Forexample, in a case where the scintillator 5 is a quadrangular prism, theincident surface may also be square and where the shape of thephotoreceiving element is square, the emission surface may also besquare, and various shapes may be considered. Further, the crosssectional shape of the surface in parallel with the emission surface isnot restricted to the circle or the like, and various shapes such as asquare or hexagonal shape may be considered.

Third Embodiment

FIG. 9 is a view for explaining a third embodiment. Identical portionsor portions having identical functions with those of the firstembodiment are not explained. Further, portions carrying identicalreference numerals are those portions having similar functions. Thedifference from the first embodiment is that a side prism 3 e isprovided to a light guide 3 having a bent portion 3 f. FIG. 9 is acrosssectional view taking notice on the bent portion 3 f and the side prism3 e. The shape of the light guide 3 of this embodiment is identical withthe light guide which has been explained with reference to FIG. 6(b) inthe second embodiment except for the portion provided with the sideprism 3 e.

FIG. 9(a) is an example of providing a side prism 3 e to a position ofthe incident surface 3 a to which the scintillator 5 is not faced. Theportion is at the top end in the direction of the major axis of anellipse of the incident surface 3 a to which light is scarcely incident,and it gives no effect on the shape of the light guide subsequent to theincident surface 3 a, thus also on light guidance. Accordingly, in acase of providing the side prism 3 e to the position, the shape of thelight guide subsequent to the incident surface 3 a and the side prism 3e can be optimized independently.

Provision of the side prism 3 e provides an advantageous effect ofimproving the light utilization efficiency. As described in the firstembodiment with reference to FIG. 4, the side prism 3 e can be modifiedinto various forms. Particularly, the light utilization efficiency canbe improved effectively by providing a reflection member to the surfaceof the reflection surface 3 e 2. Reference numeral RayS7 shows anexample of light.

FIG. 9(b) is an example of providing a side prism 3 eo also to the outerbent portion 3 f 1, and the outer side prism 3 eo has two or morereflection surfaces since it is necessary to rotate the propagationdirection of light by about 180 degrees and reflect light to theemission surface. That is, the side prism 3 ec has a reflection surfaceshape of reflecting light twice or more. FIG. 9(b) shows an example ofhaving aside prism incident surface 3 eo 1 facing the side 5 d of thescintillator 5 for incidence of light from the side 5 b, reflecting thelight substantially in the normal line direction at the incident surface3 a at the reflection surface 3 eo 2 and reflecting light at thereflection surface 3 eo 3 substantially in the direction of the emissionsurface 3 b. Such a configuration provides an advantageous effect ofimproving the light utilization efficiency. However, in a case of theouter side prism 3 eo, since it changes the cross sectional shape 3 f 1,this given an effect on light guidance. Accordingly, it is preferred toreduce the shape so as not to generate remarkable light leakage underthe effect of the side prism 3 eo and not to lower the light utilizationefficiency as a whole. Further, it is preferred, for example, that thereflection surface 3 eo 3 is formed to a continuous shape as far as asubstantially identical position with that of the incident surface 3 aas a portion of the cross sectional shape 3 f 1 as in the crosssectional shape 3 f 1′ shown by the dotted line. Reference numeral RayS8is an example of light.

A modification of FIG. 9(b) is to be described with reference to FIG.10. FIG. 10(a) is a cross sectional view taking notice on a bent portion3 f and a side prism 3 e. This modification and the example of FIG. 9(b)are different in the configuration in that a gap is provided between theouter side prism 3 eo and the bent portion 3 f. As described above,since modification to the cross sectional shape 3 f 1 gives an effect onlight guidance, the gap is provided so as not to give the effect. Lightincident from the incident surface 3 a is guided under reflection on thecross sectional shape 3 f 1 and 3 f 2, while light incident from theside prism incident surfaces 3 e 1 and 3 eo 1 is guided under reflectionon the side prisms 3 e and 3 eo.

FIG. 10(b) is a cross sectional view for explaining the side prism 3 eomore specifically. Light is incident from a surface 3 eo 1 facing thescintillator, reflects on the reflection surfaces 3 eo 2 and 3, emitsfrom the side prism emission surface 3 eo 4 facing the bent portion 3 fand is then incident to the bent portion 3 f. For the reflectionsurfaces 3 eo 2 and 3 eo 3, various modifications are possible asexplained in first embodiment with reference to FIG. 4. For example, thereflection surface 3 eo 2 and the reflection surface 3 eo 3 may beformed as a continuous curved surface. In this case, it may suffice thatthe curved surface has a function of reflecting light substantially inthe direction of the normal line on the incident surface 3 a andsubsequently, reflecting light substantially in the direction of theemission surface 3 b. Provisions of a reflection member such as ofaluminum to the reflection surfaces 3 eo 2 and 3 eo 3 can improve thelight utilizing efficiency effectively.

Further, while the portion between the side prism emission surface 3 eo4 and the bent portion 3 f is entirely shown as a gap, the portion maybe partially joined. For example, a portion of the side prism emissionsurface 3 eo 4 nearer to the incident surface 3 a may be joined with thebent portion 3 f. This is because the effect of light incident from theincident surface 3 a on the light guidance is small if the joint portionis small.

The outer side prism 3 eo and the light guide 3 may be integrated butthey may be formed separately and the side prism 3 eo may be attached tothe light guide 3 for providing the gap.

FIG. 10(c) is a perspective view in the direction of observing theincident surface 3 a. FIG. 11 (a) is a view of a light guide observedfrom the direction of an arrow a (in the direction of the normal line atthe incident surface 3 a). FIG. 11(b) is a view observing in thedirection of the arrow b in the drawing and FIG. 11(c) is a viewobserving in the direction of the arrow c in the drawing. Referring toFIG. 11(a), it can be seen that the side prisms 3 e and 3 eo arearranged along the scintillator 5 (shown by dotted line). A gap AIR ispresent between the incident surface 3 a and the outer side prism 3 eo.

The configuration of this modification provides an advantageous effectof improving the light utilization efficiency while eliminating theeffects of the incident light from the incident surface 3 a on lightguidance due to provision of the side prism 3 eo.

Next, another modification is to be explained with reference to FIG. 12showing the cross section at a plane S1. This modification is a casewhere one curve is present in the cross sectional shape of the bentportion 3 f. A portion of light incident from the incident surface 3 areflects on the cross sectional shape 3 f 1, is incident to a linearportion 3 h, and then guided as in the example of light RayF12. Aportion of light incident from the side prism incident surface 3 eo 1reflects on the reflection surface 3 eo 2, reflects on the reflectionsurface 3 eo 3 joined continuously with the curved surface of the bentportion 3 f, and is then guided to the emission surface 3 b as in theexample of light RayFS9. Light incident from the side wall 3 e 1′ isguided to the emission surface 3 b as in the example of light RayS10. Inthis modification, omnidirectional light emitted from the scintillator 5can be taken into and guided through the light guide 3 by providing acurved surface facing the incident surface 3 a, an incident surface 3 a,a containment space surrounded with a side prism incident surface 3 eo 1and a side wall surface 3 e 1′, and a side prism 3 eo 1 to provide anadvantageous effect of improving the light utilization efficiency. Thecontainment space of this modification has light incident surfacesfacing all the surfaces that emit light of the scintillator 5 andprovides an advantageous effect of improving the light utilizationefficiency also by having a light incident surface facing a portion ofthe light emission surface of the scintillator 5.

Then, another modification is to be described with reference to FIG. 13illustrating a cross section at the plane S1. This modification has sucha configuration that photoreceiving elements 4 are disposed on both leftand right sides at a certain cross section and a light guide 3 isbiforked at a position facing a scintillator 5 for propagating light toboth sides. This modification has a cross section 3 f 1 which is rightto left symmetry with respect to a center line CL1 passing the center ofthe scintillator 5. Because of the right to left symmetry, it ispossible to reduce the angle of rotating the propagation direction oflight incident from the incident surface 3 a (substantially within 90degrees). Generally, as the angle of rotating the light propagationdirection is larger, it is more difficult to reflect light so as toreach the photoreceiving element 4 and light leaking from the lightguide 3 is increased. Accordingly, by making the cross section 3 f 1 ofthe bent portion left to right symmetry with respect to the center lineCL1, an advantageous effect of improving the light utilizationefficiency is provided. This is a configuration where side prismincident surfaces 3 e 1 are arranged facing the sides 5 d on both sidesof the scintillator 5. Examples of light incident to respectivephotoreceiving elements 4 on both right and left sides were described asRayS11 and RayS12. In each of the examples, light is incident from eachof the side prism incident surfaces 3 e 1, reflects on the reflectionsurface 3 e 2, and then reflect successively on the cross sectionalshape 3 f 2 or 3 f 1, reflects on the linear portion 3 h 2, and are thenincident from the emission surfaces 3 d to the photoreceiving element 4.Also in the configuration where the photoreceiving elements 4 arearranged on both right and left sides, the light utilization efficiencycan be improved by the configuration having the side prisms. In thisconfiguration, light rotated by 180 degrees for the propagationdirection by the side prism 3 e is not or scarcely present. Accordingly,since the angle of rotating the propagation direction of light is small,an advantageous effect of improving the light utilization efficiency isprovided. Further, since the side prism 3 eo disposed to the outer bentportion 3 f 1 shown in FIG. 9(b) is not present, the outer bent portion3 f 1 and the side prism 3 e can be optimized independently to providean advantageous effect of improving the light utilization efficiency. InFIG. 13, a tilted portion is not present between the cross section 3 h 1in the linear portion and the cross section 3 f 1 in the bent portion,but it may be configured to increase the radius of curvature in thecross section 3 f 1 in the bent portion to improve the light utilizationefficiency and have a tilted portion.

In view of the above, a configuration of providing photoreceivingelements 4 on both sides as viewed for a certain cross section providesan advantageous effect of improving the light utilization efficiency.Further, the reflection surface 3 e 2 can be in various shapes asexplained with reference to the first to third embodiments 3. In a casewhere the scintillator 5 has a doughnut-like shape where particles suchas a primary electron beam 100 are passed through along the center lineCL1, a through hole may be provided along the center line CL1 of thelight guide 5. For the through hole, various shapes such as circle orsquare form may be considered. Explanation has been made in the firstembodiment to the third embodiment, but matters described above may beproperly combined and combination thereof may sometimes provide a highereffect.

With the constitutions described above, the light utilization efficiencycan be improved.

REFERENCE SIGNS LIST

-   1 electron microscope-   2 electron source-   3 light guide-   4 photoreceiving element-   5 scintillator-   6 signal particle control plate-   50 sample-   60 electron optical column-   61 sample chamber-   100 primary electron beam-   101 secondary particle

The invention claimed is:
 1. A charged particle beam device comprising:a scintillator; a light guide having an incident surface configured toincident alight from the scintillator, an emission surface configured toemit a light incident from the incident surface, and a first surfaceconfigured to guide the light incident from the incidence surface to aside of the emission surface; and an electron optical system configuredto be bent to the scintillator, wherein secondary particles or tertiaryparticles emitted from a sample incident to the scintillator, the lightguide has a bent portion, a surface of the bent portion has a curvedouter surface which is a curved surface outside of the bent portion ofthe light guide and is starting from an end of the incident surface, andthe curved outer surface has a tangential line leaning to the incidentsurface side from a normal line on the incident surface at a contactbetween the curved outer surface and the incident surface.
 2. A chargedparticle beam device comprising: a scintillator; and a light guidehaving an incident surface configured to incident a light from thescintillator, an emission surface configured to emit a light incidentfrom the incident surface, and a first surface configured to guide thelight incident from the incidence surface to a side of the emissionsurface, wherein the light guide has a bent portion, and the bentportion has a surface that guides the light to the side of the emissionsurface in a region above the emission surface in a vertical direction.3. A charged particle beam device comprising: a scintillator; and alight guide having an incident surface configured to incident a lightfrom the scintillator, an emission surface configured to emit a lightincident from the incident surface, and a first surface configured toguide the light incident from the incident surface to a side of theemission surface, wherein the light guide has a bent portion, and thebent portion has a second surface configured to guide the light to theside of the emission surface in regions excluding a region between theincident surface and the emission surface.
 4. The charged particle beamdevice according to claim 3, wherein the region between the incidentsurface and the emission surface is the region between a surfaceincluding the incident surface and a surface including an end portiondistant from the incident surface of the emission surface, and whereinthe surface including the end portion far from the incident surface ofthe emission surface is parallel to the incident surface.
 5. The chargedparticle beam device according to claim 3, wherein the first surface hasa curved outer surface starting from an end of the incident surface, andthe curved outer surface has a tangential line leaning to the incidentsurface side from a normal line on the incident surface at a contactbetween the curved outer surface and the incident surface.
 6. Thecharged particle beam device according to claim 5, wherein ascintillator containment space including the incident surface and a sidewall surface having a surface direction in the direction different fromthe incident surface and a reflection surface configured to reflect alight incident from the side wall surface are formed.
 7. The chargedparticles beam device according to claim 6, wherein the reflectionsurface is of a shape that reflects the light twice or more.
 8. Thecharged particle beam device according to claim 5, wherein a curvedsurface is present to a portion of the light guide between the incidentsurface and the emission surface.
 9. The charged particle beam deviceaccording to claim 5, wherein the curved outer surface has a portionconfigured to approximate with an equation of a circle and a center ofthe circle is not present in a plane parallel with the incident surface.